s390/topology: Add config option to switch to vertical during boot

By default, all systems on s390 start in horizontal cpu polarization.
Selecting the new config option SCHED_TOPOLOGY_VERTICAL allows to build
a kernel that switches to vertical polarization during boot.

Acked-by: Heiko Carstens <[email protected]>
Tested-by: Mete Durlu <[email protected]>
Signed-off-by: Tobias Huschle <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

Author: tobias-huschle

arch/s390/Kconfig

@@ -513,6 +513,14 @@ config SCHED_TOPOLOGY
 	  making when dealing with machines that have multi-threading,
 	  multiple cores or multiple books.
 
+config SCHED_TOPOLOGY_VERTICAL
+	def_bool y
+	bool "Use vertical CPU polarization by default"
+	depends on SCHED_TOPOLOGY
+	help
+	  Use vertical CPU polarization by default if available.
+	  The default CPU polarization is horizontal.
+
 source "kernel/Kconfig.hz"
 
 config CERT_STORE

arch/s390/kernel/topology.c

@@ -674,6 +674,8 @@ static int __init topology_init(void)
 		set_topology_timer();
 	else
 		topology_update_polarization_simple();
+	if (IS_ENABLED(CONFIG_SCHED_TOPOLOGY_VERTICAL))
+		set_polarization(1);
 	register_sysctl("s390", topology_ctl_table);
 
 	dev_root = bus_get_dev_root(&cpu_subsys);